合成路线1

Condensation of dimethyl aspartate (II) with benzyloxy carbonyl sarcosine (I) using DCI gave dimethyl benzyloxycarbonyl sarcosylaspartate (III). Removal of benzyloxycarbonyl function from (III) by catalytic hydrogenation or HBr-AcOH followed by cyclization, effected by storage over P2O5 in vacuo for 48 h, gave methyl (1-methyl-2,5-dioxopiperazin-3-yl)acetate (IV). When (IV) was reacted with ethylamine in a sealed tube for 36 h, it yielded N-ethyl-2-(1-methyl-2,5,dioxopiperazin-3-yl)acetamide (V). The compound (V) was reduced with LiAlH4 to give 1-methyl-3-(2-ethylamino)ethylpiperazine (VI). When (VI) was condensed with ethyl chloroformate (A) at pH 3-3.5, a mixture of monocarbamates (VIIa, VIIb) were obtained. Cyclization of the monocarbamates (VIIa, VIIb) were effected by treatment with sodium ethoxide to afford 3-ethyl-8-methyl-1,3,8-triazabicyclo[4.4.0]decan-2-one (centperazine). When (VI) was reacted with ethyl chloroformate (A) in the presence of NaOC2H5 or Et3N, the dicarbamate (VIII) was formed.